1. Field of the Invention
The present invention relates to corrosion inhibition. More particularly, the present invention relates to corrosion inhibition in aqueous systems. Still more particularly, the present invention relates to a composition and method for controlling corrosion in aqueous systems.
2. Description of the Prior Art
Numerous chemical additives and combinations of additives have been proposed for inhibiting corrosion in cooling systems in industrial manufacturing processes, commercial and institutional air condition systems and the like. Among such corrosion inhibitors may be mentioned such well known chemicals as chromates, zinc, nitrites, silicates, nitrates, polyphosphates and benzoates, among others. Currently, various phosphonic acids and phosphonocarboxylic acids are favored, either alone or in combination with each other, with or without other known corrosion inhibitors. For example, U.S. Pat. No. 4,246,103 discloses various phosphonic and diphosphonic acids as corrosion inhibitors while U.S. Pat. Nos. 4,052,160 and 4,057,511 claim the same function for various phosphonocarboxylic acids. A combination of a phosphonic acid and an orthophosphate as a corrosion inhibitor is disclosed in U.S. Pat. No. 3,837,803 while a scale inhibiting composition comprising a phosphonocarboxylic acid and polymaleic anhydride is disclosed in U.S. Pat. No. 4,351,796. Corrosion inhibiting combinations of a phosphonic acid and a phosphate, together with an acrylic or methacrylic polymer, are shown in U.S. Pat. Nos. 3,992,318 and 4,105,581, while U.S. Pat. No. 4,317,744 shows similar compositions in which the phosphate has been replaced with tolyltriazole, a particularly effective non-ferrous metal corrosion inhibitor.
More recently, U.S. Pat. No. 4,406,811 has disclosed a corrosion inhibiting composition for use in aqueous systems, particularly those having multiple metallurgies, comprising a combination of a triazole and an aliphatic mono- or di-carboxylic acid. Optionally, there may be incorporated in this composition as a scale inhibitor a combination of a diphosphonic acid and a phosphonocarboxylic acid. The scale inhibiting combination of the diphosphonic acid and the phosphonocarboxylic acid is disclosed in U.S. Pat. No. 3,959,168 as a sequestering agent for which a synergism is claimed.